Switchable Mirror Research Articles

Voltage‐Controlled Surface Wrinkling of Elastomeric Coatings

Wrinkling of elastomeric coatings by an electric field is reported. The associated changes in the coating's optical properties yield switchable mirrors and windows. The field Ec needed to induce wrinkling is a factor of 4.4 lower than the theoretically predicted value, which is attributed to space-charge injection.

Hydrogen Induced Modifications of Optical and Electric Properties in Mg Thin Films

A series of Mg thin films with different thickness from 10 nm to 200 nm were prepared and hydrogenated. The transmission spectrum and sheet resistance before and after hydrogenation were measured. The transmission increased from nearly zero to 16 %, the maximal changes happened at 561 nm was 17.6% with 50 nm thickness of Mg thin film, and its sheet resistance increased from 2.3 to 75.2Ω/. The results show that the Mg thin films changed obviously from shiny, metallic films to transparent, insulating films. The attractive phenomenon might enlighten the investigation and be of particular interest for switchable mirrors.

Digital Micromirror Devices: Principles and Applications in Imaging

A digital micromirror device (DMD) is an array of individually switchable mirrors that can be used in many advanced optical systems as a rapid spatial light modulator. With a DMD, several implementations of confocal microscopy, hyperspectral imaging, and fluorescence lifetime imaging can be realized. The DMD can also be used as a real-time optical processor for applications such as the programmable array microscope and compressive sensing. Advantages and disadvantages of the DMD for these applications as well as methods to overcome some of the limitations will be discussed in this article. Practical considerations when designing with the DMD and sample optical layouts of a completely DMD-based imaging system and one in which acousto-optic deflectors (AODs) are used in the illumination pathway are also provided.

Controllable light filters using an all-solid-state switchable mirror with a Mg-Ir thin film for preterm infant incubators

We have fabricated a controllable light filter using an all-solid-state switchable mirror incorporating a Mg-Ir thin film for use in preterm infant incubators. The solid-state switchable mirror device was fabricated by depositing a multilayer on a glass substrate. The mixed hydride of MgH2 and Mg6Ir2H11 created from the Mg-Ir thin film is red in the transparent state. The optical switching speeds between the reflective and transparent red states depended on applied voltage. The device showed three states, namely, reflective, black, and transparent red, due to the properties of the switchable mirror material. These results suggest that the material could be used as a controllable light filter for preterm infant incubators, since it eliminates the light wavelength that disturbs regular sleep-wake cycles of preterm infants.

Fast hydrogen-induced optical and electrical transitions of Mg and Mg-Ni films with amorphous structure

Amorphous Mg and MgNix (x = 0.03–0.30) films were prepared and their optical and electrical transitions upon hydrogen loading/unloading at room temperature were investigated. The results show that amorphous films have faster optical and electrical transitions than corresponding crystalline ones. Amorphous structure greatly facilitates hydrogen diffusion, resulting in not only preventing the formation of blocking hydrides layers but also changing the rate-controlling step from hydrogen diffusion for crystalline film to the reaction between hydrogen and Mg and/or Mg-Ni phases. We envision that amorphization is generally applicable to improve hydrogen-induced response characteristics of switchable mirror thin films.

Si incorporated diamond-like carbon film-coated electrochromic switchable mirror glass for high environmental durability

Abstract Electrochromic switchable mirror glass is promising for energy-saving windows because it changes between a reflective and a transparent state when a voltage is applied. In our previous work, we confirmed that the device degraded at high temperatures and high relative humidity using an accelerated degradation test. The degradation was related to the reaction of the moisture in atmosphere with the surface optical switching layer of the Mg–Ni thin film. Therefore, we have developed a device with a Si incorporated diamond-like carbon thin film surface layer to improve the environmental durability. When the device was kept in a simulated environment at a constant temperature of 40 °C and a constant relative humidity of 60%, optical and atomic force microscopy showed that the surface did not degrade. Moreover, the surface coating repelled water, which prevented the reaction of the moisture with the Mg–Ni thin film. The optical switching speed from the transparent state to the reflective state of the device was slower than that of the uncoated device because of the fabrication conditions. The result seems to be related to the surface of the Mg–Ni layer which might be damaged by the conditions.

Electrochemical and structural characterization of sputter-deposited Mg–Nb and Mg–Nb–Al–Zn alloy films

Nanocrystalline Mg–Nb and Mg–Nb–Al–Zn alloy films were deposited by dc magnetron sputtering on glass and quartz substrates in a wide range of niobium concentrations from 6 to 80 at.%. Structural, electrochemical and corrosion properties of the films were studied by X-ray diffraction, dc voltammetry, electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance. Development of body-centred cubic Nb structure in the Mg–Nb alloy matrix yielded the effects of lattice contraction, grain refining and electrochemical passivity. The measurements showed high corrosion resistance of the films in alkaline solutions when niobium content was one third or more. An increased corrosion resistance was achieved by introducing minor amounts of Al (ca. 2 at.%). In particular, such Al effect was pronounced at lower Nb concentrations (20 to 30 at.%). Semiconductor properties of spontaneously formed oxide on Mg–Nb alloy were studied by Mott–Schottky plots, which indicated highly doped n-type oxide structures on Mg–Nb surface. The paper fills some gap in understanding of niobium–magnesium systems, which show potential for applications in hydrogen storage, switchable mirrors and corrosion protection.

透明と鏡状態がスイッチングできる調光ミラーガラス

透明と鏡状態がスイッチングできる調光ミラーガラス

Development of switchable mirror glass

Development of switchable mirror glass

Electrochromic switchable mirror glass fabricated using adhesive electrolyte layer

We have developed a simple process for fabricating electrochromic switchable mirror glass using an adhesive electrolyte layer. The adhesive electrolyte layer was a mixture of polyethyleneimine electrolyte and polyvinyl butyral adhesive dissolved in gamma-butyrolactone. The device was formed from two substrates; the adhesive electrolyte layer was applied to one of the substrates before they were stuck together. The applied voltage required to change the state of the device was smaller than that of a conventional device with a solid electrolyte layer deposited by sputtering. Our method is simple, fast, and efficient and can be used to fabricate large devices.

Improved durability of electrochromic switchable mirror with surface coating in environment

Electrochromic switchable mirrors can be reversibly changed between a reflective state and a transparent state by applying a voltage. In our previous work, the properties of the device were significantly affected by environmental factors such as temperature and relative humidity. In that work, the effects on the device properties were investigated through an accelerated degradation test in a thermostat/humidistat bath at a constant temperature of 40 °C and a relative humidity of 80%. The switching speed between the reflective state and transparent state increased as the duration of the simulated environmental exposure increased. The device stored for 7 days under the simulated environmental conditions showed a around 45-fold slower switching speed than that of the as-prepared device. In this work, a high-durability surface coating material constructed from a cyclo olefin polymer sheet and ultraviolet resin was developed to protect the device from environmental degradation. The device with surface coating kept under the simulated environmental conditions for 7 days showed almost the same switching speed as the as-prepared device with the surface coating.

First-principles study of hydrogen ordering in lanthanum hydride and its effect on the metal-insulator transition

We discuss the structural details and the ordering of hydrogen in LaH${}_{x}$ for $2\ensuremath{\leqslant}x\ensuremath{\leqslant}3$. To this end, we combine first-principles calculations with the cluster-expansion method. This approach allows us to follow the H occupation of the interstitial sites within the face-centered cubic matrix of La atoms. We find that LaH${}_{x}$ clearly favors the fluorite structure at $x=2$ and adds excess H atoms at the octahedral interstitial sites. The ground-state behavior of the system is discussed and is found in agreement with experimentally observed structures at compositions LaH${}_{2.25}$ and LaH${}_{2.50}$; an additional ground state at composition LaH${}_{2.71}$ is predicted. The cluster expansion also permits an extensive scan of LaH${}_{x}$ structures with two octahedral vacancies per unit cell. For energetically favorable configurations, this scan yields a vacancy percolation threshold at LaH${}_{2.75}$ that possibly drives the concentration-dependent metal-insulator transition: The band gap calculated for isolated vacancy pairs disappears for percolating vacancy chains. This transition from metallic to insulating state is also experimentally observed near to the composition LaH${}_{2.8}$ and gives rise to the ``switchable mirror'' phenomenon.

Environmental durability of electrochromic switchable mirror glass at sub-zero temperature

Electrochromic switchable mirrors are expected to be used in energy-saving windows because their optical properties can be changed by application of a voltage. For practical use, the negative impact of environmental conditions on the optical switching properties of the device should be minimized. In this work, the durability of an electrochromic device was investigated in a thermostat/humidistat chamber at −5°C. After devices were stored at sub-zero temperatures, the switching speed and maximum transmittance decreased only slightly with increasing exposure time. In other words, degradation of the device did not significantly occur at sub-zero temperatures. In comparison, the optical switching properties of a device stored at 40°C and 60% relative humidity severely deteriorated. This deterioration was attributed to the degradation of the surface of the Mg4Ni optical switching layer. This layer was affected by the environmental conditions, and in particular changed from the metallic magnesium state to a non-metallic state. In future work, we will investigate suitable measures for preventing environmental damage to the device.

Electrochromic switchable mirror glass with controllable reflectance

An electrochromic switchable mirror glass with controllable reflectance was developed. The conditions for fabricating InGaZnO4 (IGZO) thin film, which serves as a transparent conductor, were investigated. The mirror glass with IGZO thin film exhibited multiple colors arising from interference between multilayers. The mirror glass with IGZO thin film fabricated at a working pressure of 0.4 Pa showed high transmittance (63%) in the transparent state and low reflectance (16%) in the reflective state at a wavelength of 670 nm. Moreover, the developed mirror glass had low glare in the reflective state because the reflection of direct, bright light was reduced.

Composition Dependence of Pd–Ag Alloy Proton Injection Layer on Optical Switching Properties of Electrochromic Switchable Mirror

We fabricated electrochromic switchable mirror glass with a Pd­Ag alloy proton injection layer to investigate the relationship between the composition of the proton injection layer and the optical switching properties, in an attempt to reduce the cost and the amount of palladium used in the fabrication of these devices. The composition of the layer was easily controlled by co-sputtering of palladium and silver metal targets with various power ratios. A device with a Pd86Ag14 layer showed the maximum transmittance in the transparent state, and similar switching speed between the reflective and transparent states to a palladium-only reference device. Changing the silver content in the layer effectively controlled the reflectance of the device. The maximum reflectance in the reflective state increased with increasing silver content, due to the high reflectance of silver. However, the maximum transmittance in the transparent state decreased, and the high silver content prevented smooth switching of the device. In this work, although Pd86Ag14 displayed the best properties as a proton injection layer, the performance was insufficient for commercial use. Therefore, more suitable fabrication conditions and proton injection materials will be the subject of future investigation. [doi:10.2320/matertrans.M2011177]

調光ミラーガラスの開発

調光ミラーガラスの開発

Switchable mirror based on Mg–Zr–H thin films

A Mg–Zr thin film is prepared on a glass substrate by co-sputtering of Mg and Zr targets and in situ sputtering of a thin Pd overlayer. The structural and optical properties of Mg–Zr and Mg–Zr–H thin film are investigated induced by hydrogen absorption and/or desorption at room temperature. Optical transmission and reflection data indicated that Mg–Zr–H thin film is the color-neutral in the visible range with chromaticity coordinates of x = 0.3566 and y = 0.3430. The formation of the ternary hydride Mg 0.82Zr 0.18H 2 is confirmed in an Mg-rich Mg–Zr solid solution thin film in the hydride state. The hydrogen insertion and extraction occurs in fcc lattice structure. Because the volume change according to hydrogenation and dehydrogenation, the switching durability is much better than that of the switchable mirror using Mg–Ni alloy.

Effects of Thin Film Deposition on Fabrication of Switchable Mirror

In this paper we studied switchable mirrors for application to transparent flat panel displays. The typical structure of switchable mirror has configuration of MgNi/Pd/Ta2O5/HxWO3/ITO. In this study photocatalyst layer (TiO2 or Nb2O5) was used between Pd and Ta2O5 layers. These layers were prepared by RF magnetron sputtering method utilizing TiO2 and Nb2O5 targets under various conditions and their electrochromic properties were investigated by using FE-SEM, EDAX and Nano View system. The transmittances of the Nb2O5 and the TiO2 thin films, could be optimized in the switchable mirror as photocatalyst layer, where they were deposited under the power of 80 W and 70 W, respectively, by the RF magnetron sputter. The characteristics of Nb2O5 and TiO2 transmittance are the outstanding at 80 W, 70 W respectively.

Degradation Analysis of Electrochromic Switchable Mirror Glass Based on Mg–Ni Thin Film at Constant Temperature and Relative Humidity

An electrochromic mirror glass that can be switched between reflective and transparent states by voltage application is presented. For the practical applications of such a device such as in energy-saving windows, optical devices, and electronic devices, the effects of environmental factors such as temperature and humidity on the optical switching properties of the device should be investigated in detail. In this work, the effects of constant temperature and relative humidity conditions on the device properties were studied. In particular, surface analysis studies were conducted. When these devices were kept at 40 °C and 60% relative humidity (RH), the speed of switching from the reflective state to the transparent state decreased with increasing time of storage in the bath. This reduced switching speed was related to the degradation of the surface metallic layers of the device, which could be observed by transmission electron microscopy (TEM) as an increase in surface roughness (Ra = 19.8 nm). Although the as-prepared device had a Mg4Ni optical switching layer approximately 40 nm in typical thickness, the degraded device exhibited an expanded layer of approximately 78 nm thickness. This increased thickness was associated with the change to the nonmetallic states of oxide and hydroxide from the metallic states of magnesium and nickel in the layer because of the adverse effects of the atmosphere.

Degradation Analysis of Electrochromic Switchable Mirror Glass Based on Mg–Ni Thin Film at Constant Temperature and Relative Humidity

An electrochromic mirror glass that can be switched between reflective and transparent states by voltage application is presented. For the practical applications of such a device such as in energy-saving windows, optical devices, and electronic devices, the effects of environmental factors such as temperature and humidity on the optical switching properties of the device should be investigated in detail. In this work, the effects of constant temperature and relative humidity conditions on the device properties were studied. In particular, surface analysis studies were conducted. When these devices were kept at 40 °C and 60% relative humidity (RH), the speed of switching from the reflective state to the transparent state decreased with increasing time of storage in the bath. This reduced switching speed was related to the degradation of the surface metallic layers of the device, which could be observed by transmission electron microscopy (TEM) as an increase in surface roughness (Ra = 19.8 nm). Although the as-prepared device had a Mg4Ni optical switching layer approximately 40 nm in typical thickness, the degraded device exhibited an expanded layer of approximately 78 nm thickness. This increased thickness was associated with the change to the nonmetallic states of oxide and hydroxide from the metallic states of magnesium and nickel in the layer because of the adverse effects of the atmosphere.